Method for promoting light emission efficiency of LED using nanorods structure

ABSTRACT

Method for the light emitting diode (LED) having the nanorods-like structure is provided. The LED employs the nanorods are subsequently formed in a longitudinal direction by the etching method and the PEC method. In addition, the plurality of the nanorods is arranged in an array so that provide the LED having much greater brightness and higher light emission efficiency than the conventional LED.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a light emitting diode (LED) structure, moreparticularly to a LED structure by employing the nanorods-like structureto raise the light emission efficiency.

2. Description of the Prior Art

Due to the one of the character light emitting diode (LED) is the highlight emission efficiency, thus there is the higher potential to becomethe illumination equipment of the new generation. However, if thepresent illumination equipments are going to be totally substituted, thelight emission efficiency of LED will be highly raised, so that the highbrightness LED brightness can be made. One of the best solutions is toproduce the nanorods-like structure for LED.

In the prior art, the nanorods-like structure formed in LED can be usedto release the stress, and reduce the piezoelectric effect. Theformation of the nanorods-like structure can also increase thesidewall-surface area to raise the light emission efficiency.

However, most of the nanorods-like structure is formed directly by thecrystal growth in materials science. For example, The hydride vaporphase epitaxy (HVPE) or the formation of GaN-nano-rod can be used. Inaddition, the etching technology can also be used to produce thenanorods-like structure, such as using E-Beam and Inductively CoupledPlasma (ICP) method to produce the nanorods-like structure. Howeverthese methods can not produce the nanorods-like structure in which theelectric current can be injected to generate the light emittingcomponent with nanorods-like structure.

For the technology disclosed in the previous literature, there is a U.S.Pat. No. 7,132,677B2 about “Super bright light emitting diode ofnanorods array structure having InGaN quantum well and method formanufacturing the same”. The GaN-based nano-rod having quantum wellstructure is used in this patent. The gap among nano-rod is filled bySpin-On Glass (SOG), and only p-type semiconductor is exposed at thetop. The metal layer is coated to form ohm contact and to get lightemitting element. Though the nanorods-like structure generated by thestructure can be used to excite the LED, the epitaxy is utilized to formthe mechanism of nanorods-like structure. The hydride vapor phaseepitaxy (HVPE) is different from the metal organic chemical vapordeposition (MOCVD) for the formation of LED, there will be havetechnical problem in future application.

In addition, the conventional light emitting component withnanorods-like structure can not be formed as good LED, because theetching surface of nanorods-like structure high resistance value.

SUMMARY OF THE INVENTION

The invention relates to a process employing the photoelectric chemistry(PEC) method to manufacture the LED with the nanorods-like structure. Inthe process firstly, a mask layer is formed on a primary layer, and theannealing way is used to form as the mask layer distributed on theprimary layer with the plurality of nano level particle masks.

The etching technology is used to etch the part which is not shielded bythe particle mask. After etching, the residual particle mask is removedto form the nanorods-like structure on the original primary layer. Thenthe PEC technology is used. Sequentially the nanorods-like structure isput in the photoelectric oxidization solution, a constant potential isapplied and is irradiated by a halogen lamp. The area irradiated by theray will be to form the oxide layer. Finally, a metal layer is coated toconduct the original primary layer without oxidation.

The feature of the invention is the nanorods-like structure formed inthe LED is different from the nanorods-like structure formed by theconventional epitaxy technology. The semiconductor process is used toproduce the nanorods-like structure on the surface of epitaxy to raisethe light emission efficiency of LED.

Further more, the conventional light emitting component withnanorods-like structure can not be formed as the good and useful LEDproducts, due to the etching surface of nanorods-like structure has highresistance value. The invention employs the PEC and etching technologyto form the LED element which can be excited by the electricity.

In the invention, under the condition of direct electrical current, theelectrical current will not leak from sidewall, so that the leakagecurrent will not be generated.

Due to the semiconductor process of LED is quite mature, the inventionis not only much suitable for the mass production, but also can reducethe manufacturing cost of LED with high brightness.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of thisinvention will become more readily appreciated as the same becomesbetter understood by reference to the following detailed description,when taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is the diagram schematically illustrating the embodiment of theinvention;

FIG. 2 is the diagram schematically illustrating the magnification ofthe invention by the Scanning Electronic Microscope (SEM);

FIG. 3 is the measuring data of the invention; and

FIG. 4 is the measuring data of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The following is a description of the present invention. The inventionwill firstly be described with reference to one exemplary structure.Some variations will then be described as well as advantages of thepresent invention. A preferred method of fabrication will then bediscussed. An alternate, asymmetric embodiment will then be describedalong with the variations in the process flow to fabricate thisembodiment.

The invention is a method to use the nanorods-like structure to raisethe light emission efficiency of LED. Firstly, the PEC technology isused to oxidize the exposed multiple quantum well in nanorods and n-typesemiconductor materials. Thus the nanorods are insulated except thep-type semiconductor at the top. Then the conductive material is coatedon un-oxidation p-type semiconductor to be formed ohm contact, in orderto produce the LED element which can be excited by the electricity.

The invention particularly uses the nanorods-like structure formed onthe LED, and employs the PEC technology to form an oxide layer aroundthe nanorods, in order to get the LED element which can be excited bythe electricity. The process for the method to use the nanorods-likestructure to raise the light emission efficiency of LED is described asthe followings.

As shown in FIG. 1A, the invention provides a LED structure, whichcomprises a sapphire substrate 101, a n-type GaN 102 formed on thesapphire substrate 101, a multiple quantum well (MQVV) 103 formed on then-type GaN 102, and a p-type GaN 104 formed on the multiple quantum well103.

Still as shown in FIG. 1B, the metal coating technology is used to coata thin nickel layer 105 on the p-type GaN 104 of LED structure. Thepreferred thickness is about 50 Å to 150 Å, and about 100 Å will bebetter for the invention.

As shown in FIG. 1C, the rapid heat treatment (RTA) is conducted for theLED structure coated with nickel. The preferred temperature is about750□ to 950□, and about 850□ will be better the invention. The preferredtime is about 30 seconds to 120 seconds, and about 60 seconds in theinvention. Therefore the plurality of nickel nano level particles 105can be formed.

Again, as shown in FIG. 1D, the plurality of nickel nano level particles105 is used as the mask. The inductively coupled plasma-reactive ionetching (ICP-RIE) technology (dry etching) is used to etch the p-typeGaN 104 and the multiple quantum well 103. The plurality of nickel nanolevel particles 105 can be used as the mask to form the plurality of thenanorods-like structure. The nanorods-like structure would comprise themetal particle 105, the p-type GaN 104 and the multiple quantum well103. The etching conditions are as follows: the gas flow rateCl₂/Ar=50/20 sccm, the applied power of plasma and bias is 400 W and 100W, respectively, the pressure is 5 mTorr in the chamber, and the etchingtime is 2 minutes. After the nanorods-like structure is formed, it isimmersed in the etching solution of nitric acid at 100□ for 5 minutes,in order to remove the residual nickel particle. And part of thenanorods-like structure is removed as the electrode.

As shown in FIG. 1E, the Photo-electrochemical (PEC) process isconducted. At first, the LED with the nanorods-like structure is fixedon the cathode of a circuit, there put into the photoelectric chemicaloxidization solution (such as deionized water). Then, 20 V of voltage isintroduced. 300 W of mercury lamp is used to conduct the oxidizationreaction. After 10 minutes, except the part of p-type semiconductor, allarea irradiated by the mercury lamp is to form an oxide layer (Ga₂O₃)106.

Finally, as shown in FIG. 1F, a nickel/gold layer 107 is coated, whichforms the ohm contact having the exposed p-type semiconductor layer(p-type GaN) 104. Meantime, the chromium/gold is coated on the electrodeto form the electrode metal 108, in order to form the LED having thenanorods-like structure.

The invention uses the photoelectric chemical oxidization technology toform the LED with the nanorods-like structure which can be excited bythe electricity. In the process, the thickness of nickel can be alteredto change the size of metal nano level particles, in order to determinethe diameter of nanorods after the etching process.

During the ICP-RIE, the etching time can be altered to change the depthof nanorods. The oxidization time, applied voltage, and light strengthof PEC can also be altered to change the thickness of oxidization layer.

The invention is verified by the experiment, and FIG. 2 shows themagnification of the invention by the Scanning Electronic Microscope(SEM), which reveals the filling of nanorods after the PEC oxidization.As shown in FIG. 3, the measuring data of the invention is revealed. Itdescribed the spectrum of photo-excited light for as-grown LED, nanorodsLED with PEC and nanorods LED without PEC.

As shown in FIG. 4, the measuring data of the invention is revealed. Itdescribed the spectrum of electro-excited light for as-grown LED andnanorods LED with PEC.

It is understood that various other modifications will be apparent toand can be readily made by those skilled in the art without departingfrom the scope and spirit of this invention. Accordingly, it is notintended that the scope of the claims appended hereto be limited to thedescription as set forth herein, but rather that the claims be construedas encompassing all the features of patentable novelty that reside inthe present invention, including all features that would be treated asequivalents thereof by those skilled in the art to which this inventionpertains. If the line pattern is used as the shape of mask, thetriangular tunnel will be formed first in the etching process, then theside wall of tunnel will be closed to separate the gallium nitride fromthe semiconductor substrate. If the dot pattern or random pattern isused as the shape of mask, the hexagonal cone will be formed first inthe etching process, then the thick gallium nitride film will separatefrom the semiconductor substrate.

It is understood that various other modifications will be apparent toand can be readily made by those skilled in the art without departingfrom the scope and spirit of this invention. Accordingly, it is notintended that the scope of the claims appended hereto be limited to thedescription as set forth herein, but rather that the claims be construedas encompassing all the features of patentable novelty that reside inthe present invention, including all features that would be treated asequivalents thereof by those skilled in the art to which this inventionpertains.

1. A method for raising the light emission efficiency of the LED usingthe nanorods-like structure, comprising: providing a LED structurehaving a sapphire substrate, a p-type GaN layer formed on the sapphiresubstrate, a multiple quantum well layer formed on the p-type GaN layer,and a n-type GaN layer formed on the multiple quantum well layer,forming a thin metal layer on the surface of n-type GaN layer and rapidheat treating the thin metal layer to form a plurality of metalparticle; etching the n-type GaN layer and the multiple quantum welllayer, the plurality of metal particle being used as the mask to form aplurality of nanorods, the plurality of the nanorods-like structurecomprises the plurality of metal particle, the n-type GaN layer and themultiple quantum well layer, removing the residual plurality of metalparticle being removed, the nanorods-like structure being used as theelectrode; processing a photo-electrochemical process to form an oxidelayer to encapsulate the plurality of the nanorods-like structure; andcoating a metal layer on the oxide layer as an ohm contact between theelectrode and the p-type GaN layer to form the LED having thenanorods-like structure.
 2. The method according to claim 1, wherein thethin metal layer comprises the nickel metal.
 3. The method according toclaim 1, wherein the metal coating technology is used to form the thinmetal layer.
 4. The method according to claim 1, wherein the temperaturefor rapid heat treating is about 750□ to 950□.
 5. The method accordingto claim 1, wherein the time for the rapid heat treatment is about 30 sto 120 s.
 6. The method according to claim 1, wherein the etching methodcomprises the dry etching.
 7. The method according to claim 1, whereinthe PEC process comprises using the mercury lamp to conduct theoxidization reaction.
 8. The method according to claim 1, whereincoating a metal layer on the oxide layer, the metal layer comprisesnickel (Ni)/gold (Au) and chromium (Cr)/platinum (Pt).
 9. A method forraising the light emission efficiency of the LED using the nanorods-likestructure, comprising: providing a sapphire substrate, a p-type GaNlayer formed on the sapphire substrate, a multiple quantum well layerformed on the p-type GaN layer, and a n-type GaN layer formed on themultiple quantum well layer forming a thin metal layer on the surface ofn-type GaN layer; processing a rapid heat treatment to form a pluralityof metal particle; etching the n-type GaN layer and the multiple quantumwell layer, using the plurality of metal particle as a mask to form aplurality of nanorods, the plurality of the nanorods-like structurecomprises the plurality of metal particle, the n-type GaN layer and themultiple quantum well layer, removing the residual plurality of metalparticle, the removed nanorods-like structure being used as anelectrode; processing the photo-electrochemical process for forming ametal layer to encapsulate the plurality of nanorods-like structure; andcoating a metal layer on the oxide layer as an ohm contact between theelectrode and the p-type GaN layer to form the LED having thenanorods-like structure.
 10. The method according to claim 9, whereinthe thin metal layer comprises nickel metal.
 11. The method according toclaim 9, wherein the metal coating technology is used to form the thinmetal layer.
 12. The method according to claim 9, wherein thetemperature for rapid heat treating is about 750° C. to 950° C.
 13. Themethod according to claim 9, wherein the time of the rapid heattreatment is about 30 s to 120 s.
 14. The method according to claim 9,wherein the etching method comprises the dry etching.
 15. The methodaccording to claim 9, wherein the PEC process comprises using themercury lamp to conduct the oxidization reaction.
 16. The methodaccording to claim 9, wherein a coating metal layer on the oxide layer,the metal layer comprises nickel (Ni)/gold (Au) and chromium(Cr)/platinum (Pt).